Device and Method for Needle/Catheter Location Utilizing Correlation Analysis

ABSTRACT

An apparatus and method to enable clinicians to verify needle or catheter location within an anatomic site by relying upon combined sensing of two signals, such as a pressure signal and a heart rate pulse signal, in which the detection of a correlation between both signals is identified to confirm location of the needle or catheter.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods fordetermining needle or catheter location in a patient utilizing acorrelation analysis, and more particularly, but not exclusively, tocorrelation analysis, such as comparison of beats-per-minute orcross-correlation of waveforms, of objective pressure in the needle orcatheter and the patient's heart rate pulse.

BACKGROUND OF THE INVENTION

Currently, when measuring pressure within a needle or catheter, there isno ability to identify false-positives of a cardiac pulsewave detectedin the needle or catheter as opposed to pressure changes which trulyrepresent the cardiac pulsewave. As used herein cardiac pulsewave isdefined to mean a pressure waveform which contains a signal whichoriginates from the contraction of the heart or vessels, and thereforecontains information representing, the cardiac pulse. It is conceivablethat a needle or an indwelling catheter can detect a non-cardiacpulsation from a variety of non-cardiac sources within the body,including respiratory changes, muscle movements of the diaphragm, etc,and can falsely report that detected pulsation as the cardiac pulsewave.It is also conceivable that patient bodily movements, such as posturalchanges in position of the patient, could produce pressure changes thatare measured and are misinterpreted as originating from thecardiovascular system. In particular, existing devices do not include anindependent means to verify that a particular pressure waveform is fromthe heart, and thus cannot rule out false positives in which thedetected waveform has come from a source other than the cardiovascularsystem. At the same time, determining the location or the patency of aneedle or catheter is of great interest to the clinician, such as fordelivering of a drug to a patient. Hence, the ability to ensure that thepressure being sensed is not confused with other pressure changing wavesproduced in the body is of great interest if one is to rely on thisinformation as indicative of needle or catheter placement, which, inturn, will impact patient outcome.

For example, in clinical use, after the placement of a needle orcatheter it is common to deliver a dose of medication. Subsequentadministrations through a needle or catheter can be compromised due topotential blockage of the needle or catheter, or by migration of aneedle or catheter from the original position. Therefore, catheterassessments may be required including determining if a catheter isclogged, determining if the catheter is fully functional, anddetermining if the catheter has moved from the initial location. Theinability to accurately differentiate a catheter's function leaves theclinician in a serious and sometime dangerous quandary: is the failuredue to effectiveness of the drug, movement of the catheter, a cloggedcatheter from precipitate or a blood clot?

The data also show that between 10 to 25% of all catheters need to bereplaced on patients because of catheter migration after placement.Clinicians have difficulty determining the reason for the failure of acatheter. Typically it takes to 20 to 30 minutes to evaluate catheterfunction and placement as the clinician waits for an observation to atherapeutic drug response, because currently this is the only means toevaluate catheter function. This adds additional risks and additionalcosts to healthcare systems, as a non-functional catheter can requirelife-threatening time to assess. Thus, the difficulties and potentialrisks of catheter placement and monitoring are serious challenges, andtherefore a predictable manner to differentiate these conditions wouldbe of great value to patients and clinicians.

Even so, existing devices developed to detect pulsatile waveforms can beexpensive and complicated to use, requiring the use of anelectro-mechanical motor to deliver the fluid to the patient. Suchdevices do not allow a clinician to observe an objective pressuregenerated while manually infusing a drug using a handheld syringe as istypically or preferably done. Existing systems are also not designedwith inputs from multiple sources to separately compare and analyze botha heart-beat and pulsatile pressure waveform during use, and so do notprovide two distinct physiologic sources of heart rate to determine andverify needle or catheter location. As such, the inventors, in arrivingat the present invention, have recognized deficiencies in prior artdevices and methods for needle or catheter placement, such as theability to: 1) detect an input source of a cardiovascular system inwhich the heart-rate is used for direct comparison with needle orcatheter location; 2) detect a cardiovascular response via a directfluid path and analyze the information in the fluid path to producebeats-per-minute analyses to compare to a secondary source which isknown to be detecting a heartbeat; 3) correlate and analyze more thanone signal to determine that a needle or catheter is properly placedwithin an anatomic location; and 4) to provide a positive alert whenthese two signals are correlated within a range to confirm atrue-positive.

Therefore, there is a need in the art for inexpensive and simple devicesand methods that are capable of eliminating false-positives whenlocating a needle or catheter in the body which devices and methodswould be of great value to the clinician and to the treatment ofpatients.

SUMMARY OF THE INVENTION

In view of the above-noted and other needs, in one of its aspects thepresent invention may provide devices and methods which use two or moredifferent physiologic sources indicative of the cardiac pulse todetermine needle or catheter placement prior to medication delivery orfluid aspiration. One of the sources may be the cardiac pulsewavedetected as a pressure waveform in the needle or catheter, such as by anin-line pressure sensor, and a second source may be heartbeat detectionfrom a finger pulse sensor, for example, or other location known to emitthe cardiac pulsewave or heartbeat. The two physiologic sources may thenbe compared to verify that the pressure waveform detected in the needleor catheter is in fact the cardiac pulsewave, thus eliminatingfalse-positive indications of the cardiac pulsewave in the needle orcatheter. The comparison may be performed as a correlation analysis ofsignals from the two different physiologic sources to determine if thefrequency of the signals from the two different physiologic sources isclinically comparable. The correlation analysis may be performed as acomparison of the numerical value of heart rate in beats-per-minute asdetected at each of the two or more different physiological sourcesand/or by cross-correlation of waveforms detected at each of the two ormore different physiological sources, for example. Thus, the presentinvention can perform “Needle/Catheter Location Correlation Analysis” asa comparison of two or more cardiovascular signals which may includebeats-per-minute, cross-correlation of pressure waveforms, and/orobjective pressure measurements, for example, to determine the locationof a needle or a catheter within a mammalian body.

Positive verification of the cardiac pulsewave in the needle or cathetermay establish both the correct position of the needle or catheter andits patency. As a result, devices and methods of the present inventioncan allow clinicians to more easily assess in real-time proper needle orcatheter placement with confidence, due to the verified detection of thecardiac pulsewave. These may be presented to the clinician as a signalor an alert confirming proper needle or catheter placement. As a result,with the verified real-time detection of the cardiac pulsewave in theneedle or catheter the clinician may use a manual syringe rather than anautomated mechanical pump such that the clinician can personallyposition the needle and control the delivery of medication or aspirationof fluid and the accompanying physical force applied to the syringe.More precise control of the physical force by the clinician can alsoprevent catheter movement from excessive pressures. Excessive pressureduring medication delivery could cause the dislodgement of the needle orcatheter from a site as uncontrolled fluid pressures produce a“jet-stream” at the tip of the catheter or needle.

In another of its aspects, devices of the present invention may providea clinician with an objective (i.e. measured) pressure value in theneedle or catheter during the flushing stage. Knowing the objectivepressure as a medication is injected can also assist the clinician inavoiding excessive force, preventing excessive pressures. For example,the present invention may alert the clinician when a pressure value hasbeen exceeded. The alert can be audible, visual, haptic or the like.

Exemplary uses of devices and methods of the present invention mayinclude locating a needle within the body to a specific target site,such as that of an epidural procedure or peripheral nerve block. Inparticular the identification of the epidural space, the determinationof needle proximity to a neurovascular bundle in regional peripheralnerve blocks, and other medical procedures which require a needle orcatheter tip to be positioned at a specific location (e.g., intrathecal,intravenous, intra-arterial, organ of the body) where the cardiac pulseis present, all can benefit from devices and methods of the presentinvention. Accordingly, the use of devices and methods of the presentinvention at such exemplary target sites can with greater reliabilityreplace the current Loss-of-Resistance technique (LOR-technique).Further to its advantages, devices and methods of the present inventionmay be used for all types of needles and catheters that are placed intopatients at anatomic sites at locations that emit a rhythmic pulsationof the arterial system, and may be provided as an inexpensive andportable system.

In still further of its aspects the present invention may achieve anumber of objectives. For example, an objective of the invention may beto detect a pulsatile waveform of a catheter which is verified for thepresence of a cardiovascular pulse by comparing a first input to asecond input from the cardiovascular system, such as a heartbeatdetected from a second input source. The redundant nature of these twosources may be identified and confirmed electronically and produce analert to the operator. A further objective of the present invention maybe to provide an inexpensive device to determine an objective pressurevalue that is generated when a drug is injected through a catheter usinga manual syringe to prevent excessive pressure production at the tip ofa catheter that might dislodge the catheter from a target position.Devices of the present invention can enable an audible alert to be setfor a maximum pressure value to alert the operator if they have exceededa specific pressure value. In addition, a further objective may be todetect and display a pulsatile pressure waveform corresponding to thepulse of the cardiac-vascular system to determine the position of acatheter. A further objective of the invention may be to provide amethod and device that can detect the pulsatile pressure waveform thatis present in the epidural space or intrathecal space of the centralnervous system and detecting a pulsatile waveform or the proximity tothe neurovascular bundle of nerve. A further objective may be to observean objective pressure and graph an objective pressure value over time tomonitor the response to an injection performed with a manual syringe todetermine the patency of a catheter. Another objective may be tocorrelate an objective pressure value with a pulsatile pressure waveformto determine the patency and position of a catheter by simultaneouslyviewing the pressure/time graph and the pulsatile pressure waveform todetermine catheter function. A further objective may be to provide amean value of a pulsatile pressure waveform from an intravenous catheterto determine the patency of said catheter before, after and during aninfusion.

In particular, in a first exemplary configuration, the present inventionmay provide an apparatus for confirming placement of a hollow-borestructure at a desired treatment location in a mammalian subject. Theapparatus may include a first sensor operably connected to a lumendisposed in the hollow-bore structure; the first sensor may beconfigured to provide a first signal in response to detection of a firstproperty indicative of a cardiac pulse in the lumen of the hollow-borestructure. The apparatus may include a second sensor configured toprovide a second signal in response to detection of a second propertyindicative of the cardiac pulse. A controller may be operably connected(wireles sly or wired) to the first and second sensors to receive thefirst and second signals, and maybe configured to compare the first andsecond signals to provide a comparison result, whereby the comparisonresult provides an indication of placement of the hollow-bore structurerelative to the desired treatment location. The first and/or secondphysical property may be one or more of a pressure, change in fluidvolume, an electrical signal, and an optical signal. The first andsecond properties may relate to the same physical property or differentphysical properties indicative of the cardiac pulse. The hollow-borestructure may include one or more of a needle and a catheter. The firstsensor may include an in-line pressure sensor having a sensor lumendisposed in fluid communication with the lumen of the hollow-borestructure, and the second sensor may be a finger pulse sensor. One ormore of the first and second sensors may include a memory configured tostore an indication that the first or second sensor, respectively, hasbeen used. The device may also include an identification circuitembedded within or connected to one or more of the first and secondsensors, wherein the identification circuit is configured to provide asignal to the controller, the signal including one or more of: aconfiguration signal indicative of physical characteristics of the firstor second sensor; a verification signal indicative of the first orsecond sensor; and a use signal so that the controller can detect thenumber of times or length of time the first or second sensor waspreviously used.

In a second exemplary configuration the present invention may provide anapparatus for confirming placement of a hollow-bore structure at adesired treatment location in a mammalian subject having a controllerconfigured to receive a first signal from a first detector placed at thetreatment location. The first signal may be indicative of a cardiacpulse in the hollow-bore structure. The controller may also beconfigured to receive a second signal indicative of the cardiac pulsefrom a second detector placed at a second location. The controller maybe programmed to compare the first and second signals to provide acomparison result, whereby the comparison result provides an indicationof the placement of the hollow-bore structure relative to the desiredtreatment location.

For both the first and second (or other) exemplary configurations, thefirst and/or second signal may represent one or more of a pressure,change in fluid volume, an electrical signal, and an optical signal. Thefirst signal may have a first period and the second signal may have asecond period, and the controller may be configured to compare the firstand second periods to provide the comparison result. (In addition, thefirst signal may include a waveform having a first period and the secondsignal may include a waveform having a second period, and the controllermay be configured to compare the first and second periods to provide thecomparison result.) Further, the first signal may include a firstnumeric value indicative of a frequency of the first signal, and thesecond signal may include a second numeric value indicative of afrequency of the second signal, and the controller may be configured tocompare the first and second numeric values. One or more of the firstand second numeric values may be a cardiac pulse in beats-per-minute.The controller may also be programmed to perform a cross-correlationanalysis of the first and second signals. The controller may beconfigured to create an alert signal when the comparison result iswithin a selected value. In addition, a display may be operablyconnected to the controller for receiving one or more of the first andsecond signals and the comparison result from the controller. In onedesirable configuration, the controller may include the display. Thedisplay may include a first data section for displaying a pressuredetected by the first sensor in the lumen disposed in the hollow-borestructure, and may include a second data section for displaying thefirst and second signals. The first and second signals may each includea respective waveform, and the second data section may include a graphdisplaying the respective waveforms of the first and second signals. Thedisplay may also include a section for displaying an alert indicationwhen the comparison result is within a selected value. The alert may beone or more of an auditory, visual, and haptic signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description ofexemplary embodiments of the present invention may be further understoodwhen read in conjunction with the appended drawings, in which:

FIG. 1 schematically illustrates an exemplary configuration of a devicefor needle or catheter location in accordance with the present inventionin which both a controller and display device are used;

FIG. 2 schematically illustrates a further exemplary configuration of adevice in accordance with the present invention in which a separatecontroller is not used;

FIG. 3 schematically illustrates additional aspects of the devices ofFIGS. 1 and 2;

FIG. 4 schematically illustrates an exemplary configuration of a displayof a prototype in accordance with FIG. 1 of the present invention, inwhich the display shows objective pressure over time and cardiacpulsewaves and pulse detected from two independent sources, along withnumerical display in real-time of clinically useful parameters ofobjective pressure and the numerical pulse rates of each of the twoindependent sources, along with an indicator showing whether or not thetwo independent sources are correlated in frequency (i.e., that the twoindependent sources both relate to the cardiac pulse);

FIG. 5 schematically illustrates details of an exemplary operation ofthe devices of FIGS. 1-3;

FIG. 6 illustrates a circuit diagram of an exemplary configuration ofthe controller of FIG. 1;

FIG. 7 illustrates a flow chart of an exemplary method of operating thedevice of the present invention;

FIG. 8 illustrates a method for performing signal correlation inaccordance with the present invention; and

FIG. 9 illustrates a further method for performing signal correlation inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, wherein like elements are numbered alikethroughout, FIGS. 1, 2 schematically illustrate exemplary configurationsof devices 100, 150 of the present invention for determining properplacement of a hollow-bore structure, such as a needle 302 and/orcatheter 310, at a selected treatment location in a patient 20 using atleast two independent measurements of the cardiac pulse, one of whichmeasurements is detected via the hollow-bore structure. For example, thedetection of the cardiac pulse via the needle 302 and/or catheter 310may be accomplished by sensing a physical property in the lumen of theneedle 302 and/or catheter 310, such as a physical property representingthe pressure or fluid volume change in the lumen, where the variation inthe pressure or fluid volume change contains a signal created by, andindicative of, the cardiac rhythmic contraction, e.g. the cardiacpulsewave. In particular, an in-line pressure sensor 300 may be providedin fluid communication with, and between, the needle 302 (or catheter310) and a manual, handheld syringe 200, FIGS. 1, 2.

The second of the two independent measurements may be detected by asecond device, such as a finger pulse sensor 400, disposed at a locationon the patient 20 at which a physical property representing the cardiacpulse may be detected, FIG. 2. The physical property may be a pressure,an electrical signal, an optical signal, or other suitable signal, forexample, that provides for independent verification of the presence ofthe cardiac pulse detected in the needle 302 and/or catheter 310. Thephysiologic location of the second device 400 may be different from thatof the needle 302 and/or catheter 310.

Through the use of two independent measurement sources 300, 400 for thecardiac pulse, devices 100, 150 of the present invention can compare thesignals from the two separate sources 300, 400 to confirm that thesignal from the needle 302 and/or catheter 310 is indeed the cardiacpulse, which in turn will confirm that the needle 302 and/or catheter310 is in the “correct” location for procedures in which the targettissue is one in which the cardiac pulse is expected to be present. Forexample, target sites for correct needle or catheter placement in whichthe cardiac pulse is expected to be present include the epidural space,intrathecal space, or proximate to a neurovascular bundle or otheranatomic structure that emits a pulsatile wave produced by thecardiovascular system, including the heart itself.

Once confirmation of needle or catheter placement is confirmed by thedevice 100, 150, an alert may be provided to the clinician, and theclinician may proceed with injection or aspiration through the syringe200, depending on the nature of the procedure being performed. The alertmay be provided in any suitable form, such as auditory, visual, orhaptic, for example. Thus, devices of the present invention are capableof location guidance and confirmation during the placement of a needle302 and/or catheter 310. Indeed, devices and methods of the presentinvention may confirm patency of the needle 302 and/or catheter 310.

Turning to FIG. 1 in more detail, operation of the sensors 300, 400 maybe provided by a dedicated controller device 500. The controller device500 may be operably connected to the sensors 300, 400 via respectivecables 210, 410, and in certain cases an adapter 212 may be providedbetween the controller device 500 and a respective cable 210.Alternatively, the sensors 300, 400 may communicate wirelessly with thecontroller device 500, via any suitable communications technology suchas Bluetooth® communication. The sensor 300 disposed in sensingcommunication with the needle 302 and/or catheter 310 may, as describedabove, be an in-line pressure sensor whose fluid path is continuous withthe needle 302 and/or catheter 310, such as a Merit Medical, MER200. Insuch a case, the contraction of the heart produces propagation of anenergy wave representative of the cardiac pulse into a fluid in thesensor 300 and the wave may be measured through pressure or volumetricchanges therein. The changes may produce a repetitive signal in the formof a pulsewave signal and may be measured from peak-to-peak or zerocrossings to determine the frequency of the pulsewave signal to yieldthe cardiac pulse rate in beats-per-minute. Alternatively, the sensor300 could be positioned alongside the catheter 310 and/or could beinterposed between an external fluid source such as an IV bag, syringeor any vessel that provides a continuous fluid line.

In addition, the sensor 300 (and/or sensor 400) may be one or more of anacoustic sensor, optical sensor, infrared detector or other device whichdetects the cardiac pulse which has propagated within tissues from thecardiovascular system to the location of the sensor 300, 400. In short,any sensor type capable of detecting the cardiac pulse in the lumen ofthe needle 302 and/or catheter 310, whether by pressure, sound, or otherphysical property, may be used as the sensor 300. Similarly, any sensortype capable of detecting the cardiac pulse at a physiologic sourceindependent of the lumen of the needle 302 and/or catheter 310 may beused as the sensor 400 including one based on photophelthysmography(PPG) such as a Model 3231 USB or Model 3230 Bluetooth® Low Energy fromNonin® Medical, Inc, for example. Alternatively, the sensor 400 may beprovided as a pneumatic inflatable cuff (such as that found in asphygmomanometer). With a preference for using non-invasive methods fordetecting the heart beat or beats-per-minute of the peripheral vascularsystem, it is also possible that the detection of the heart beat couldbe from an electronic signal that is captured with a heart-rate monitorin contact with the skin of a patient.

One or more of the sensors 300, 400 may also be provided in the form ofa single use sensor which may be particularly desirable in the casewhere the sensors 300, 400 come in direct contact with bodily tissues orfluids, e.g. blood, cerebrospinal fluid, or fluid filled epidural space.For example, the sensor 300 may include a separate body fluid pressuresensor 305 and a microchip in the form of a programmable memory 320,FIG. 3, where the programmable memory 320 may be used to track usage ofthe sensor 300 and thereby limit the sensor 300 to a single use.Information communicated with the sensor 300 and memory 320 may beencrypted and coded to ensure security of the use of the sensor 300.Alternatively or additionally, sensor 300 can have an internal on-chiptimer that allows a specified amount of time for use of the sensor,after which the sensor 300 expires. These features mitigate thepotential for use on multiple patients and help to control againstcounterfeit products. The sensor 400 may be similarly configured forsingle use.

The data collected from the sensors 300, 400 may be transmitted to thecontroller device 500 for further processing, after which the processeddata may be transmitted via a cable 4 or wirelessly to a display device600, such as a computer, smart phone, tablet, or other handheld device,for viewing by the clinician, FIG. 1. The controller device 500 mayinclude a circuit board, central processor unit, rechargeable battery,connectors for wired communication, and/or antennas for wirelesscommunication via Wi-Fi, Bluetooth® or other suitable communicationsstandard. The controller device 500 may both process the received dataand control and provide power to the sensors 300, 400. The displaydevice 600 may also further process the data prior to display and mayinclude a variety of input elements such as buttons, a touchscreen,voice activated commands, scanning, etc. to transfer information intothe controller device 500. Alternatively, the display device 600 mayreceive the data directly from the sensors 300, 400 and control theoperation of the sensors 300, 400 so that a separate controller device500 is not required, FIG. 2. In this regard, the display device 600 mayinclude a software application that can collect, process and displayinput data received from the two or more separate input sources 300, 400with or without use of the controller device 500. The data to bedisplayed by the display device 600 may include, but is not limited to,an objective pressure value 630, a graph of objective pressure over time610, and a pulsatile waveform 620 representative of the contractivenature of the heart or cardiovascular system, FIG. 2. A prototype of thedevice controller 500 was constructed for use in the system 100 of FIG.1.

Prototype Controller Circuit

FIG. 6 illustrates a schematic of the circuit 550 used in the prototypecontroller 500 of FIG. 1. (The circuit 550 also represents at thecomponent-level implementation of block diagram elements shown in FIG.3. Reference to corresponding elements of FIG. 3 are providedparenthetically.) As shown in FIG. 6, two different communicationoptions were provided, and both were tested: wireless communications viaBluetooth® transceiver U2 (e.g., transceivers 532, 534, FIG. 3), anddirect wire communications via the USB serial data cables 210, 410, FIG.1, connected to connector J1, FIG. 6. (Specifications for all componentsof the circuit 550 are provided in Table 1 below.) The prototype 100collected data from the two sensors 300, 400 and provided the data tothe controller 500 where the data were formatted for presentation to auser.

In the prototype 100, a Nonin Medical, Inc Xpod® 3012LP External OEMPulse Oximeter with 8000A Reusable Finger Clip pulse oximetry sensor wasused for the finger pulse sensor 400. The finger pulse sensor 400produced a continuous stream of serial data which were input onconnector J3. The data from the finger pulse sensor 400 were provided tothe unit serial input receiver channel 1 at pin 38 of a microprocessorU3 (e.g., microprocessor 520, FIG. 3). A standard baud rate transmissionwas used which was set by resistor R16. The data were collected andassembled into a format simplified for use by the display device 600.

The in-line pressure sensor 300 was a piezoresistive bridge design ModelMER200 from Merit Medical, Inc and was attached to connector J4, FIG. 6.The reference voltage used to power the in-line pressure sensor 300 wasprovided directly from the lithium-ion battery BT1 in the circuit 550.The in-line pressure sensor 300 was connected through an adapter 212,FIG. 1. The adapter 212 had several functions: to easily connect thesensor 300 to the controller 500 through an RJ12 quick connectionconnector J12; to provide power turn-on by interlock connection to thebattery BT1; and, to permit identification and use management of thein-line pressure sensor 300 by a one-wire memory device.

A memory device 320 may be present in the in-line pressure sensor 300,FIG. 3, to identify and serialize the in-line pressure sensor 300allowing traceable data to be collected and stored by the display device600. In the prototype such a memory device was in the adapter 212. Useof the memory device 320 could also help mitigate the potential for useof the pressure sensor 300 on multiple patients. The sensor 300 andadapter 212, FIG. 1, may be disposable components intended for singleuse on one patient.

Since the device 100 had a user accessible connector J4, the circuit 550included a protection against Electro-Static Discharge (ESD) eventswhich could be caused by the accumulation of excessive static charge.Diodes D4-D9 were used to clamp the inputs of connector J4 to protectthe internal circuitry, FIG. 6. The adapter 212 internally jumperedtogether pins 4 to 5 at connector J4, FIG. 6, which provided aconnection path from the internal battery BT1 negative terminal to theremainder of the components of circuit 550. Thus, the circuit 550 waspowered on when the adapter 212 was attached to the connector J4, whichalso helped mitigate exposure leakage current to users and patient whenno adapter was present. Connector J4 was also used to charge the batteryBT1 using an external charger 10 attached to J4 via cable 2, FIG. 1. Thecircuit 550 was not powered when the charger 10 was attached; only thebattery BT1 was charged. The charge current was limited and monitored toprovide protection against battery fault/fire protection.

As shown in FIG. 6, the signal from the in-line pressure sensor 300 waspresented to chip U4, a high resolution 24-Bit analog-to-digitalconverter, (e.g., A/D converter 510, FIG. 3). The analog-to-digitalconverter U4 used, for its reference voltages, the same battery/groundvoltage that powered the in-line pressure sensor 300. Hence, theanalog-to-digital converter U4 made a ratiometric measurement of thesignal from the in-line pressure sensor 300, and no correction wasneeded for gain and offset. The raw output of the analog-to-digitalconverter U4 was multiplied by a constant that was determined by thegain of the Merit MER200, which was pre-calibrated and adjusted duringmanufacturing. Resistors R14 and R15 of the circuit 550 providedmitigation for possible broken sensor leads for the in-line pressuresensor 300. In the event of a breakage, the pressure reading from theanalog-to-digital converter U4 was driven to an upper or lower extremeand thus became invalid.

The data from the analog-to-digital converter U4 were sent to themicroprocessor U3 over a serial peripheral interface (SPI) serialchannel. The data from the analog-to-digital converter U4 were assembledin 3 bytes which were re-assembled in the microprocessor U3 as a 32-Bitword representing the catheter 310/needle pressure.

The microprocessor U3 maintained some data in non-volatile memory whichincluded a device serial number, catheter gain correction, and generalhardware settings. This data could be transferred to and changed bycommands sent from the display device 600. This information was storedin EEPROM memory internal to the microprocessor U3.

While gathering the in-line pressure sensor data from theanalog-to-digital converter U4, the microprocessor U3 also attempted tomeasure the cardio-induced pulse rate, if present, in the waveformsignal from the in-line pressure sensor 300. An average value wascalculated for the waveform signal and subtracted from the raw data toprovide a zero-centered waveform. The zero-centered waveform wasprocessed to identify zero-crossings in the zero-centered waveform fromwhich the period of the peaks and valleys was determined. A measurementof the period from the peaks/valleys was made and converted into abeats-per-minute numeric value. The numeric value and the positivezero-crossing information was passed via a communication channel to thedisplay device 600. Additional details on the operation ofmicroprocessor U3 are discussed below in connection with FIG. 8.

As shown in FIG. 6, crystal Y1 was the clock source for microprocessorU3. The internal timing measurements and communication rate wereestablished from this frequency choice. The frequency was chosen toprovide sufficient computational speed while reducing radiated emissionfrom the circuit 550. The 3.7 volt battery BT1 voltage also helpedmitigate emissions. Voltage dividers consisting of R1/R2 and R9/R10scaled the voltage from battery BT1 and radio transceiver U2 to a valuein the range of the analog-to-digital converter internal tomicroprocessor U3 and allowed measurement of the supply voltages. Thisdesign was capable of operating with battery voltages below 3.0 volts.Over 12 hours of continuous operation was possible before batteryrecharging was required.

The microprocessor U3 was programmed in-circuit by attaching a standardMicrochip Technologies programmer to J2. The code could be changedin-the-field as the software design included a boot-loader section.After first programming, a production jumper JP2 may have a solderconnection placed across it to protect the circuit 550 from futureprogramming. The jumper JP2 also improves protection against ESD events.

The circuit 550 included two options for communication with the displaydevice 600. When the USB cable option was used, a Future TechnologiesDigital International (FTDI) serial-to-USB cable 4, FIG. 1, wasconnected to jumper J1 on the “b”-side, i.e., pins b2-b7. This provideddirect attachment of the cable 4 to serial channel 2 of themicroprocessor U3. The USB cable option was configured as a fullimplementation of RS-232 (TTL) using flow control CTS/RTS. The Smart USBcable 4 was powered by the display device 600 to which the USBconnection was made. Power was not provided through the circuit 550. Atthe display device 600, the USB port was configured as a virtualcommunications serial port.

For wireless Bluetooth® communication, the FTDI cable 4 was removed andjumpers were placed across pins 3-8, a-to-b of jumper J1. The choice ofcommunication baud rate was selected based on the default configurationof Bluetooth® transceiver, U3. The same baud rate was used for the FTDIUSB cable. This allowed the microprocessor U3 to operate without regardto whether the information and commands were transferred from thedisplay device 600 via USB or Bluetooth® communications.

The radio transceiver module U2 was a microchip design that simulatedserial communication to the display device 600 and was pre-certified tomeet the requirements of the FCC and EU standards for RF performance.The Green LED D2 indicated the radio transceiver module U2 was poweredwhile the Red LED D3 flashed during data transmission, FIG. 6. The modejumper JP1 was normally shorted and was used only for debuggingpurposes. Supervisory circuit U1 provided power-on and low-voltageshutdown of the radio transceiver module U2. The display device 600 wasresponsible for pairing and bonding to the transceiver antenna AE1 ofthe radio transceiver module U2. Operation of the transceiver U2occurred according to the frequencies and protocols defined forBluetooth® BLE. The radio transceiver module U2 was defined as a serverdevice providing data to a slave. The radio transceiver module U2wirelessly communicated with the display device 600, in the case of theprototype a tablet (Dell® Latitude 7200, 2-in-1 tablet), which executedthe software for analyzing and displaying the signals from the twosensors 300, 400.

Parts list for components shown in FIG. 6. Reference(s) Part NumberValue Description Manf. AE1 — Antenna PWB trace Antenna — BT1 LP503562JBLithium Ion Battery Lithium Polymer Jauch Quartz Battery 1S1P 1250 MAH3.7 V BATT LITH POLY 1S1P 1250 MAH 3.7 V C1, C4, C6, C9, ECA-1EM100B 10uf Capacitor, Aluminum, 10 UF Panasonic C11, C13, C17, 20% 25 V RADIALElectronic C18, C20 Components C2, C3, C5, C320C104K5R5TA7303 0.1 ufCapacitor, Ceramic, 0.1 uf, Kemet C10, C12, C14, 50 v, X7R Radial C15,C16, C19, C21 C7, C8 C315C220K2G5TA 22 pf Capacitor Ceramic, 22 PF Kemet10% 200 V COG RADIAL D1, D4, D5, 1N4148 1N4148 Diode, General Purpose,ON D6, D7, D8, D9 100 V 200 MA DO35 Semiconductor D2 HLMP-CM1G-350DDGreen LED GREEN CLEAR T-1 ¾ Broadcom T/H Limited D3 HLMP-1700-B0002 RedLED RED DIFFUSED T-1 T/H Broadcom Limited J1 67996-416HLF CommunicationsConnector, Header, Vert, Amphenol Option 16P0S 2.54 MM ICC (FCI) J268000-406HLF Progrm. Conn. Connector, Header, Vert, Amphenol 6POS 2.54MM ICC (FCI) J3 LX60-12S Xpod Connector Connector Receptacle 12P Hirose0.02 GOLD SMD R/A Electric Co Ltd J4 0950097667 ID Adapter Conn.Connector, CONN MOD Molex JACK 6P6C R/A UNSHLD JP1 — Mode Jumper SolderJumper, PWB trace — JP2 — Production Solder Jumper, PWB trace — JumperR1, R2, R8, R9, CFR-25JB-52-47K 47.0K Resistor 47 KOhm ¼ W 5% Yageo R10Axial R3, R7 CFR-25JB-52-470R 470 Resistor 470 Ohm ¼ W 5% Yageo AxialR4, R6, R17 CFR-25JB-52-10K 10.0K Resistor 10 KOhm ¼ W 5% Yageo Axial R5CFR-25JB-52-100K 100K Resistor 100 KOhm ¼ W Yageo 5% Axial R11CFR-25JB-52-68K 68K Resistor 68 KOhm ¼ W 5% Yageo Axial R12, R13CFR-25JB-52-1K 1.0K Resistor 1.0 KOhm ¼ W Yageo 5% Axial R14, R15CFR-25JB-52-10M 10M Resistor 10 MOhm ¼ W Yageo 5% Axial R16CFR-25JB-52-4K3 4.3K Resistor 4.3 KOhm ¼ W Yageo 5% Axial R18CFR-25JB-52-2K2 2.2K Resistor 2.2 KOhm ¼ W Yageo 5% Axial R19CFR-25JB-52-10R 10 Resistor 10 Ohm ¼ W 5% Yageo Axial U1 MCP112T-270E/MBMCP112T IC SUPERVISOR 1 CHANNEL Microchip SOT89-3 Technology U2RN4871-I/RM130 RN4871 Bluetooth ® BLE Module, Microchip shieldedTechnology U3 PIC18F87K22-I/PT PIC18F87K22-xPT IC MCU 8 BIT 128 KB FLASHMicrochip 80TQFP Technology U4 ADS1232IPWR ADS1232 IC ADC 24 BITSIGMA-DELTA Texas 24TSSOP Instruments Y1 ECS-160-S-5PX-TR 16 MHz CrystalOscillator, 16.0 MHz, ECS Inc. series resonant

Display Device

Turning to the display device 600 and signal analysis in more detail,the display device 600, working alone or in concert with the controllerdevice 500, may produce useful data and alerts to the clinician to aidin the placement of the needle 302 and/or catheter 310, includingproviding an indication of patency of the catheter 310, FIGS. 2, 4. FIG.4 schematically illustrates an actual screenshot provided on the displaydevice 600 as used with the working prototype 100 of FIG. 1, whichincluded the controller device 500 with controller circuit 550. FIG. 4provides but one exemplary output configuration for data in accordancewith the present invention.

With reference to FIG. 4, a display 450 on an LCD screen of the displaydevice 600 included two graphs. The upper half of the screen displayedan “Objective Pressure Graph” 451 and in the lower half displayed a“Pressure Waveform Graph,” 455 showing waveforms 452, 453 correspondingto data collected from the sensors 300, 400, respectively. In addition,a Dialogue Bar was provided below the Pressure Waveform Graph. These twographs can be shown simultaneously or can be displayed individually atdifferent times.

The objective pressure was displayed in both the Objective PressureGraph showing a scrolling graph of objective pressure vs. time 451 andas a real-time numeric value 401, FIG. 4. A Maximum Pressure Line wasalso displayed, which could be changed by the clinician. When theobjective pressure exceeded this line, an audible alert was sounded,though it is understood that the audible alert could have been a visualor some other type of alert. The objective pressure 401 corresponded topressure generated by the handheld syringe 200 as the clinician applieda force to the plunger of the syringe 200. The graphing of the objectivepressure data was performed on a continuous basis and in real-time, andthe scaling could be changed by pressing the Up and Down arrows (↑, ↓)on the left-hand side bar of the Objective Pressure Graph 451, whichallowed scaling to be changed in real-time. If the pressure detectedreached the Maximum Pressure Line without the expression of fluid, theclinician could conclude that the needle 302 and/or catheter 310 isoccluded. A negative slope in the Objective Pressure Graph couldindicate a dissipation of the pressure in the needle 302 and/or catheter310, further indicating that the needle 302 and/or catheter 310 was notoccluded. Thus, the real-time changes in the Objective Pressure Graphprovide vital information to confirm or rule out an occluded needle 302or catheter 310 even when the data from the waveforms 452, 453 areambiguous. Therefore, the Objective Pressure Graph provides needle orcatheter patency information in addition to the information displayed inwaveforms 452, 453.

As to the Pressure Waveform Graph 455, the waveforms 452, 453 wereconstructed using a high resolution, high-speed sampling algorithm inwhich between 30 to 90 samplings per second were taken. In theprototype, average values of the waveforms 452, 453 were calculated anddrawn to the display device 600 to maintain the waveforms 452, 453centered on the Pressure Waveform Graph. Within 4 seconds (or some otherprogrammed period of time in the software), the displayed waveform 452,453 was calculated to a mean pressure value and positioned to becentered within the graph 455 relative to the mean horizontal line 454displayed in FIG. 4.

The waveforms 452, 453 from the first and second sensors 300, 400 hadpeak-to-peak crests (and zero crossings) that were reflective of thepulsatile nature of the heart contracting and were consistent with thevalue of the number of heart beats-per-minute (bpm). The heart rate inbeats-per-minute could also be calculated from the zero crossings.However, two zero-crossings are present per beat, so either time betweensuccessive positive-slope zero crossings or time between successivenegative-slope zero crossings were indicative of heart rate. The twowaveforms 452, 453 could be visually compared on the display 450 by theclinician. In addition, a real-time numerical value 402 for the heartrate detected by the first sensor 300 was displayed, as well as thereal-time numerical value 404 for the heart rate detected by the secondsensor 400, FIG. 4. The detection of a both waveforms 452, 453 from thetwo input sources 300, 400 provides the clinician with an understandingas to the position of the needle 302 and/or catheter 310 within ananatomic structure that transmits a pulse wave from the cardiovascularsystem. Two sets of up and down arrows (↑, ↓) on the left-hand side barof the Pressure Waveform Graph were usable to scale the heights of eachof the waveforms 452, 453 individually. In addition, an audible bpm beepcould be provided which sounds with the same frequency as the pulse rateshown in either waveform 452 or waveform 453. In such a case display ofthe waveforms 452, 453 associated with the audible bpm beep could beomitted, with the audible bpm beep filling the role of providing suchinformation to the clinician.

Alternatively, the waveforms 452, 453 could be displayed in a variety ofdifferent formats. Exemplary formats may include,(and are not limitedto): a continuous waveform which may be represented as a pressurewaveform with peak-to-trough continuous line; a non-continuous line inwhich the peak-to-peak is displayed; or, a blinking light that isrepresentative of the peak-to-peak pressure values that are detected bythe input sources. In addition, it may be that the waveforms 452, 453are not both displayed but only a visual alert is provided confirmingthat the signals are coordinated with the peak-to-peak signalrepresentative of heart beats-per-minutes from the two independentsources 300, 400. For instance it is possible that neither of thewaveforms 452, 453 are displayed, and that the peak-to-peak signals arerepresented as an audible or haptic signal. Or it is possible to relysolely upon the numeric values displayed as beats-per-minute. Further,any combination of these display techniques may be used.

As shown in FIG. 4 the Dialogue Bar included (from left to right): 1) a“Zero” button to calibrate the in-line pressure sensor 300; 2) anobjective pressure value 401 for the in-line pressure sensor 300; 3)heart rate beats-per-minute (bpm), 402 from the in-line pressure sensor300; 4) a “Sync alert” 403 indicating that the heart rate values 402,404 were correlated to confirm that a single source (the heart) hasproduced both of these signals; 5) a heart rate beats-per-minute (bpm)404 from the finger pulse sensor 400; 6) an oxygen saturation value 405in percent; and 7) an “{circumflex over ( )}image{circumflex over ( )}”button to capture the image on the screen.

The display device 600 in the prototype performed an analysis todetermine whether the two waveforms 452, 453 were correlated at theirfundamental frequency, which frequency corresponded to the cardiac bpm(beats-per-minute) if the waveform 452, 453 represented the cardiacpulsewave. If not, the fundamental frequency would correspond to someother spurious signal not related to the cardiovascular system. Twosignals were considered correlated in frequency even if a phase offsetbetween the two signals were present, such as illustrated in thewaveforms 452, 453, FIG. 4. A phase offset between the signals may bepresent due to the fact that the cardiac pulse may travel throughdifferent tissue types and different distances to arrive at each of thesensors 300, 400.

If the waveforms 452, 453 were frequency-correlated, the “Sync alert”403 would flash on/off to alert the clinician that the bpm rates fromeach of the sensors 300, 400 were found to be correlated, i.e., that thefrequency of signals from the sensors 300, 400 were sufficiently matchedwithin a selected deviation, with an acceptable range of deviation of 2bpm to 15 bpm. Thus, the clinician was provided with a confirmation oflocation of the needle 302/catheter 310 at the desired location when the“Sync alert” 403 was activated. In addition, an alert may optionally besounded if the two waveforms 452, 453 were not correlated, indicatingthat the needle 302 and/or the catheter 310 was not positioned properly.Any of these alerts may be visual, audible, haptic, or any combinationthereof.

The signals detected by the sensors 300, 400 may also be analyzed by avariety of correlation techniques to determine the cardiac pulse rate,including but not limited to, waveform analysis, pulse-rate comparison(heart-rate, beats-per-minute), cross-correlation, and combinationsthereof. In yet another embodiment a cross-correlation analysis may beperformed on the data from the sensors 300, 400 producing a matchedfrequency of the two signals with time-shift producing definitivepositive correlation based on set a criteria. In this case, thecross-correlation may be the sum of the product of the two signalsshifted relative to each other over a period of not less than onecomplete cycle of the longer period waveform. In yet another embodimentauto-correlation may be used to normalize the values for betterthreshold detection comparison of the cross-correlation peak value. Inyet another embodiment the auto-correlation peak spacing can be used toverify the validity of the BPM measurements made of each sensor data.

In yet another embodiment a cross-correlation analysis may be performedon the data from the two input sources 300, 400 producing a definitivepositive correlation based on set criteria. Illustrated in FIG. 9 is anexample of a cross-correlation technique in accordance with the presentinvention that may be used to objectively determine the degree ofcorrelation of the two signals 452, 453 from sensors 300, 400. Exemplarydetails are specific to an implementation for the controllers 500 and600. For discrete data samples as collected by exemplary devices 100,150 of the present invention, the cross-correlation function may bedefined as

${{\left( {f*g} \right)(\tau)}\overset{\Delta}{=}{\sum\limits_{t0}^{{t0} + T}{\overset{\_}{f\left( {t - \tau} \right)}{g(t)}{dt}}}},$

where T is the period (number of samples) of the waveform beinganalyzed, and τ is the sliding offset between the two waveforms.

Basically, the correlation function generates a series ofsum-of-products over the entire sampled data set to come up with valuesof the correlation coefficient for each τ value. The correlationcoefficients calculated have a maximum value at shift τ_(max). Due topossible velocity propagation delays through the patient tissue, the twowaveforms 452, 453 may have an offset in the peak correlationcoefficient position, in which is τ_(max)≠0. The method 900 shown inFIG. 9 presents a representation of an exemplary method which may beused for correlation detection in accordance with the present invention.The collected data from the in-line pressure sensor 300 is input at step902. The pressure reading from the finger-sensor 400 is input at step904. The data are collected synchronously by display device 600, andhence the pair of data (902, 904) represents a single instance in time.The sampled data are placed in circular FIFO buffers 906, 908. The sizeof the buffers 906, 908 is determined by the period of the pulsewaves452, 453. The longest period occurs at the lowest pulse rate which isdefined to be 40 BPM. With a data sampling frequency of 75samples/second, a minimum of 112 samples represent one complete waveform in each buffer 906, 908. In addition, the τ shift could be up to112 samples as well. Hence, the minimum buffer size to perform acomplete cross-correlation function is 224 for the combined buffers 906,908. In this exemplary case, the buffer length may be chosen as 256,which makes circular FIFO buffer management easier and also providessome addition space in the buffers 906, 908. An extra 32 bufferpositions of padding (256−224=32) may be provided that allow new data tobe inserted into the circular buffers 906, 908 without corrupting the224 values being processed to determine the correlation coefficients.The buffers 906, 908 may be simultaneously written and read which easesthe computational burden on the microprocessor in the display device600. The computation need not be completed in a single data sample time.Real word correlation is generally a serial process of mathematicaloperations. Each new correlation check is begun at the position of thelast data written to the circular buffers 906, 908 and works backwards.

The correlation algorithm 902 may begin at the last data positionwritten and work backwards through the data from this point. Based onthe values of buffer size and assumed pulse rates, the completecomputation must finish before 32 additional data samples are taken,that is: 32 samples/75 samples/second, or 0.43 seconds. In this time 112sum-of-products are calculated. The sum-of-product, step 914, is theaccumulation of 112 multiplications 910 a-910 d of data in each buffer906, 908. Each correlation coefficient calculated at summation point 914may be temporarily stored in an array buffer 918. Each value saved isthe sum-of-product for 112 offsets of the τ parameter. The τ offset isthe starting from which data is read from the buffers 906, 908 for eachsum-of-product calculation. The array buffer 918 results may be analyzedto determine the degree of correlation between the pulsewaves. Tonormalize the cross-correlation results, auto-correlation may also beperformed. Numerically, the cross-correlation results in buffer 918should be values between +1.0 and −1.0. Values near 0.0 are consideredto be non-correlated and indicated as not “In-Sync” on the displaydevice 600. Values greater than a determined threshold are consideredsignificantly correlated and provide an indication to the clinician ofcorrect placement of the needle 302 and/or catheter 310. Should thepulse rate be greater than the minimum design value, multiplecorrelation coefficients will be produced. For example, at 80 BPM pulserate, there will be 2 correlation maximums. The correlation algorithm920 may analyze the data for maximum peak and generally select the τoffset value closer to zero. All of the selected correlationcoefficients may be output to the display device 600. The analysis mayinclude consideration of the measured BPM from each sensor 300, 400. BPMmay also be obtained by analysis of the auto-correlation measurementsmade on each waveform 452, 453. Though possibly lacking in resolutiondetail, the separation measurement of multiple peaks in auto-correlationmay be another measurement of pulse rates from each sensor 300, 400 andmaybe useful information for making the correlation detectionindication.

Controller Device Algorithm

In another of its aspects, devices of the present invention may use themethod 850 in confirming catheter or needle placement and patency, FIG.8. The flowchart of FIG. 8 represents the software logic that was usedin the prototype to calculate the beats-per-minute pulse rate asmeasured by the in-line pressure sensor 300. The software executed inthe microprocessor U3, FIG. 6, of circuit 550 of the controller device500. The software identified the zero-crossings of the cardiac pulsewavesignal 452 in the needle 302 and/or catheter 310, FIG. 4. Thebeats-per-minute rate was determined by measuring the period of timebetween successive positive zero-crossings of the pulsewave signal 452.The positive zero-crossings were selected, because the ascending aorticsystolic pressure wave has a faster rate of change and hence provides amore accurate point of measurement than the descending slope of thenegative zero-crossings. The software operated in a loop 867 using astate machine to analyze the pulsewave 452.

The state machine was initialized at step 851 when software beganexecuting, FIG. 8. The STATE variable determined which side of the meanaverage the loop 867 was last processing. A Filter Counter variable wasprovided which was incremented and decremented based on whether thedifference between measured value and the mean average was above orbelow zero. The Running Average Filter was also initialized at step 851.At step 852, the pressure reading was obtained from theanalog-to-digital converter U4 of FIG. 6. Analog-to-digital conversionswere produced by hardware events and occurred at approximately 80samples per second. A new value of the pressure sample was obtained atstep 852 and was sent to the display device 600. The new pressure samplewas also used in method 850. Specifically, the new pressure sample wasadded into the Running Average Filter by computing the running averageat step 853. The Running Average Filter output a value which was theaverage of the last 128 pressure samples. At step 854 the pressuresample had the average value subtracted to generate the Difference valuewhich was stored at step 855. Next, a decision was made at step 856 todetermine if last previous operation was looking for a positive (POS) ornegative (NEG) zero-crossing. If the STATE at step 856 was POS, then thesoftware branched to step 862 looking for a negative crossing. Thecriterion for a negative crossing was that the Difference was less (morenegative) than a negative threshold of −0.1 mmHg. If the Difference didnot meet this criterion, then the loop passed to step 866 where itwaited for the next pressure sample to repeat, via step 860, theprocessing of method 850. Returning to step 862, should the Differencemeet the criterion, then the Filter Counter was decremented, step 863.At step 864 the count value was tested to determine if the count wasless than −3. If not, control passed to step 866 and method 850 repeatedby passing to step 866 and waiting for the next sample. Normally thelast value of the Filter Counter would be +4 following the last positivezero-crossing. Hence the Filter Counter must be decremented 8 times toreach the value −4 tested, and the STATE variable was then set to NEGindicating that a descending zero-crossing was found, step 865. TheFilter Counter value was forced such that it does not exceed −4. Theloop 867 then returned to wait for the next pressure sample at step 866.

Returning to step 856, if the STATE at step 856 was NEG (i.e., not POS),that is looking for an ascending zero-crossing, the branch wouldcontinue to step 857. At step 857 a test was made to determine if thecriterion for a positive zero-crossing was met. The Difference pressuremust exceed +0.1 mmHg. If not, the method 850 repeated jumping to step866 and waited for another pressure sample. Should the criterion be met,control passed to step 857. The Filter Counter value was incremented atstep 858. Typically the counter would begin incrementing from −4 afterthe last descending zero-crossing. At step 859 the count value wastested to determine if sufficient positive differences had been found tojustify indication of an ascending zero-crossing of pressure, that isthat the count exceeded +3. If not, control passed to step 866 andmethod 850 repeated by passing to step 866 and waiting for the nextsample. Should the Filter Counter exceed +3 at step 859, then controlpassed to step 860. At step 860 the STATE variable was set to POS andthe Filter counter was limited to +4. At this point a valid positivezero-crossing had been determined. An algorithm measured the period oftime since the last positive zero-crossing occurred. The period wasmeasured in milliseconds by a time base maintained in microprocessor U3using interrupts. The period measurement was dynamically adjusted toprovide good BPM measurements. At fast heart rates greater than 200 BPM,up to 4 zero-crossings are counted to give a resolution better than 1.0BPM. At low pulse rates, below 60 BPM, a single zero-crossing periodmeasurement was performed to allow quicker updates of the measured heartrhythm. The final calculation of period was performed at step 861 andthe calculated BPM value, 402 in FIG. 4, was sent to the processcontroller 600 for display to the user and for pulse correlationmatching with the heart rate 404.

A further understanding of how the devices 100, 150 of the presentinvention may operate with regard to generating the data for display onthe display device 600 is seen in the block diagram 800 of FIG. 5. Inthis diagram, the “cardiovascular pulse sensor device” block correspondsto the sensor 400 and the “pressure sensor device” block corresponds tothe sensor 300. Communication among the components and processes isillustrated as wireless using the conventional symbol for Bluetooth®communication, though the components and processes could communicate viaother methods such as Wi-Fi or hard wired.

The application software 803, which can run on the display device 600,can include the step 804 for writing a time/date stamp to the sensor 300to assist in ensuring that the sensor 300 is used for only a single use.As part of the operation, the software also obtains the data from thesensors 300, 400 at step 805. Collection of data continues untilcomplete, step 806, and the Bluetooth® radio is disabled, step 807.During the data collection step 805 a sub process 808 can run whichincludes functions such as creating the graphical display of thepressure 810; calculating the excessive pressure alert 811; displayingthe numerical pressure 812; performing the correlation detection of thedata received from the sensors 300, 400, step 813; and, issuing thevarious alerts 814.

In addition, an authorization scheme of the present invention mayinclude a computer chip, SIM, or other uniquely coded circuit in theadapter 212 or sensor 300, for example chip 320. The chip, SIM, or otheruniquely coded circuit may be disposed in communication with thecontroller device 500 and/or display device 600, and may be read by anauthorization program or circuit in the controller and/or display device500, 600. If the chip, SIM, or other uniquely coded circuit is genuine,the controller and/or display device 500, 600 will operate properly, ifnot, the sensor 300 may be disabled and a warning such as “unauthorizedadaptor detected” can be posted on the display device 600 and optionallya warning sound may be made, including but not limited to a vocalizationof words, an alarm, or other warning signal or any combination thereof.The coded circuit may also be coded for a one-use function whereby theauthorization program or circuit in controller and/or display device500, 600 will detect if a specific sensor 300 was previously used and,if so, again disable the controller and/or display device 500, 600 andpost a warning.

Description of an Exemplary Method

In another of its aspects, devices of the present invention may providethe clinician with a particularly useful method of confirming catheteror needle placement and patency, such as the method 700 illustrated inFIG. 7. For example, the clinician often needs to determine if acatheter is: i) clogged or functioning and/or ii) if the catheter hasmoved from the target position, collectively beginning at step 702.Making such a determination may necessitate the following actions: 1)flush the catheter to determine if it is clogged or clear and then 2)infuse a bolus of drug. In making such a determination, the clinicianmay connect an in-line pressure sensor between the catheter and asyringe used to flush the catheter, step 704, and may attach a secondaryinput source to detect a heartbeat, such as a photophelthysmographyfingertip clamshell to detect the heartbeat. The syringe and in-linepressure sensor, and any other disposables such as a catheter, may beprimed with fluid, step 706. The in-line pressure sensor and secondarysource may be operably connected, wired or wirelessly, to a displaydevice for viewing by the clinician, step 708. A maximum objectivepressure value may also be set on the handheld device and remain storedin the handheld device for future use. The maximum pressure value may beset anywhere between 75 mm/Hg to 500 mm/Hg, for example. When themaximum pressure value is reached an alert may be sounded as an audiblesound or tone. A spoken word may also be used to alert the clinicianthat the maximum pressure has been exceeded.

Signals from the in-line pressure sensor and secondary source (e.g., afinger pulse sensor) may be compared and analyzed by a controller and/ordisplay device, such as one or more of the controller 500 and displaydevice 600. If the two signals are found to be correlated in frequency(that is beats-per-minute of a heartbeat), an alert may be displayed onthe display device as a flashing box and/or an audible alert sounded,indicating that the catheter is properly positioned.

If a pulsewave is detected, step 710, the clinician may proceed withflushing the catheter, step 712. The clinician may again observe theresponse on the display device, step 714. If no response is observed andno pulsewave correlation is found between the signal from the in-linepressure sensor and the secondary input source, step 722, the pulsewavedetected at step 710 (or step 732 as described below) is afalse-positive finding. The clinician then concludes that the catheteris not properly positioned, and the catheter is removed, step 724.Alternatively, if a response is observed at step 714, and the clinicianobserves that pulsewave correlation is found between the signal from thein-line pressure sensor and the secondary input source, step 716, theclinician can bolus the patient with the drug, step 718, and observe thetherapeutic output, step 720.

Returning to the situation where no initial response is observed at step708, the clinician may observe the objective pressure graph to determinepatency of the catheter. In such a case the clinician will likely seethat no pulsewave is detected at all, step 726, but will still proceedwith flushing the catheter, step 728. Again, the clinician may observethe response on the display device, step 729. The clinician may thendetermine if the catheter is clogged by observing an absence of agradual reduction in the pressure;

this may be observed by viewing an objective pressure vs. time graph inwhich the slope of the curve demonstrates whether fluid is flowing outof the catheter and into the tissues. If the pressure does not dissipateover time, step 736, and no pulsewave correlation is found between thesignal from the in-line pressure sensor and the secondary input source,step 738, the clinician can conclude that the catheter is clogged andthe catheter may be removed, step 740. Alternatively, if a response isobserved at step 729 and the response is a reduction of pressure, step730, the clinician may observe that pulsewave correlation is foundbetween the signal from the in-line pressure sensor and the secondaryinput source, step 732. In such a case, the clinician may proceed withflushing the catheter, step 734, and may proceed with steps 714 through724 as described above. The example in the proceeding sections describethe method for use with a catheter, it is understood that a similarmethod could be used for placement of a needle within a patientperformed with the same steps described.

It is anticipated that the method 700 could be used for confirmation ofthe position of a catheter in the epidural space or the intrathecalspace, for example. In addition, the method 700 could be used todetermine when a needle or catheter is positioned properly in a vesselsuch as a vein or artery for an infusion. It is also conceivable thatsuch a system could be used for aspiration of bodily fluids in which theneedle position within a target confirmed by a pulsatile waveform isnecessary prior to the removal of said fluid such as cerebral spinalfluid from the central nervous system. The method 700 may also be usedin situations where assessing the pulsatile nature of a tissue is vital.Devices and methods of the present invention may also be used to assessthe perfusion status of vessels to a tissue or organ based on thequality (amplitude and cadence) of the pulsatile pressure waveform asseen in the pulse interval and amplitude of the waveform curve; forexample, the perfusion status may be assessed in the extremities as itrelates to diabetes, frost-bite, trauma, tissue grafting, etc.

Thus, the above disclosure describes devices and methods that canconfirm the location of a needle and/or catheter as well as the patencyof properly located indwelling catheter. The devices and methods mayprovide essential confirmation through physiologic feedback that aneedle or catheter has been positioned within an anatomic site. Devicesin accordance with the present invention may detect the presence ofcardiovascular signals from two separate input sources and determine ifthe signals are coordinated or not by analysis of the signals. Apositive-correlation may be confirmed, verifying the position of aneedle or catheter within the body and an alert may be provided inresponse. If a correlation cannot be established between the twocardiovascular signals, no alert is provided, which indicates that aneedle and/or catheter is improperly positioned.

These and other advantages of the present invention will be apparent tothose skilled in the art from the foregoing specification. Accordingly,it will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. Forexample, the apparatuses disclosed herein could incorporate a device toremotely monitor a patient, such as by Bluetooth, Wi-Fi or other deviceof transmitting the collected pressure data to the software loaded on asmartphone or computer workstation. The clinician would be able toassess the patient's condition related to the presence or absence of apulsatile waveform. A communication module, optionally present in thecontroller device 500 and/or display device 600, may relay datacollected to either an on-line external communication system or directlyto a specific communication target to relay this information for eitherreal-time or retrospective review. It should therefore be understoodthat this invention is not limited to the particular embodimentsdescribed herein, but is intended to include all changes andmodifications that are within the scope and spirit of the invention asset forth in the claims.

1. An apparatus for confirming placement of a hollow-bore structure at a desired treatment location in a mammalian subject, comprising: a needle, a catheter or combination thereof to provide the hollow-bore structure, the hollow-bore structure having distal and proximal ends with respective openings thereat; a first sensor disposed in fluid communication with the hollow-bore structure; a syringe disposed in fluid communication with the first sensor, where each of the hollow-bore structure, first sensor, and syringe have a respective fluid passageway extending therethrough with all of the fluid passageways disposed in fluid communication to provide a continuous closed fluid pathway extending from the syringe through the first sensor to the opening at the distal end of the hollow-bore structure; and a controller configured to receive a first signal in response to detection of a first property from the first sensor, the first signal indicative of a cardiac pulse in the fluid passageway of the hollow-bore structure, the first signal also indicative of an objective pressure in the fluid passageway of the hollow-bore structure, and the controller configured to receive a second signal in response to detection of a second property indicative of the cardiac pulse from a second sensor placed at a second location, the controller programmed to determine if the first and second signals are correlated to provide a comparison result, wherein controller is programmed to determine that the first and second signals are correlated at a fundamental frequency in the presence of a phase offset between the first and second signals whereby the comparison result provides an indication of placement of the hollow-bore structure relative to the desired treatment location.
 2. The apparatus of claim 1, wherein the controller is programmed to provide an alert when the objective pressure exceeds a selected value indicative of an excess pressure in the fluid passageway of the hollow-bore structure .
 3. (canceled)
 4. The apparatus of claim 1, wherein the first sensor comprises an in-line pressure sensor disposed in fluid communication with the fluid passageway of the hollow-bore structure.
 5. (canceled)
 6. The apparatus of claim 1, wherein the second sensor comprises a finger pulse sensor.
 7. The apparatus of claim 1, wherein the first property is one or more of a pressure, change in fluid volume, an electrical signal, and an optical signal.
 8. The apparatus of claim 1, wherein the second property is one or more of a pressure, change in fluid volume, an electrical signal, and an optical signal.
 9. The apparatus of claim 1, wherein the first and second properties relate to the same property.
 10. The apparatus of claim 1, wherein the first and second properties relate to different physical properties.
 11. The apparatus of claim 1, wherein the controller is disposed in wireless communication with one or more of the first and second sensors.
 12. The apparatus of claim 1, wherein one or more of the first and second sensors includes a memory configured to store an indication that the first or second sensor, respectively, has been used.
 13. The apparatus of claim 1, comprising an identification circuit embedded within or connected to one or more of the first and second sensors, wherein the identification circuit is configured to provide a signal to the controller, the signal including one or more of: a configuration signal indicative of physical characteristics of the first or second sensor; a verification signal indicative of the first or second sensor; and a use signal so that the controller can detect the number of times or length of time the first or second sensor was previously used.
 14. The apparatus of claim 1, wherein the first signal represents one or more of a pressure, change in fluid volume, an electrical signal, and an optical signal.
 15. The apparatus of claim 1, wherein the second signal represents one or more of a pressure, change in fluid volume, an electrical signal, and an optical signal.
 16. The apparatus of claim 1, wherein the first signal has a first period and the second signal has a second period, and wherein the controller is configured to compare the first and second periods to provide the comparison result.
 17. The apparatus of claim 1, wherein the first signal comprises a waveform having a first period and the second signal comprises a waveform having a second period, and wherein the controller is configured to compare the first and second periods to provide the comparison result.
 18. The apparatus of claim 1, wherein the first signal comprises a first numeric value indicative of a frequency of the first signal, and the second signal comprises a second numeric value indicative of a frequency of the second signal, and wherein the controller is configured to compare the first and second numeric values.
 19. The apparatus according to claim 18, wherein one or more of the first and second numeric values is a cardiac pulse in beats per minute.
 20. (canceled)
 21. The apparatus of claim 1, wherein one or more of the first and second signals each comprise a respective waveform having a respective period and having a respective mean value, and wherein the controller is configured to detect zero-crossings of each of the respective waveforms through the respective mean value.
 22. The apparatus of claim 1, wherein the controller is configured to create an alert signal when the comparison result is within a selected range.
 23. The apparatus of claim 1, comprising a display operably connected to the controller for receiving one or more of the first and second signals and the comparison result from the controller.
 24. The apparatus of claim 23, wherein the controller includes the display.
 25. The apparatus of claim 23, wherein the display includes a first data section for displaying a pressure versus time in the lumen of the hollow-bore structure.
 26. The apparatus of claim 23, wherein the display includes a second data section for displaying the first and second signals.
 27. The apparatus of claim 26, wherein the first and second signals each include a respective waveform, and wherein the second data section includes a graph displaying as a function of time the respective waveforms of the first and second signals.
 28. The apparatus of claim 23, wherein the display includes a section for displaying an alert indication when the comparison result is within a selected range.
 29. The apparatus of claim 28, wherein the alert is one or more of an auditory, visual, and haptic signal.
 30. The apparatus of claim 1, wherein the controller is programmed to perform a cross-correlation analysis of the first and second signals.
 31. The apparatus of claim 1, wherein the comparison result does not include comparing different respective portions of the first signal.
 32. The apparatus of claim 31, wherein controller is programmed to determine that the first and second signals are correlated by using a cross-correlation of the sum of the product of the first and second signals. 